ASTM G112-22

Standard Guide for Conducting Exfoliation Corrosion Tests in Aluminum Alloys

SIGNIFICANCE AND USE
4.1 Although there are ASTM test methods for exfoliation testing, they concentrate on specific procedures for test methodology itself. Existent test methods do not discuss material variables that can affect performance. Likewise they do not address the need to establish the suitability of an accelerated test for alloys never previously tested nor the need to correlate results of accelerated tests with tests in outdoor atmospheres and with end-use performance.  
4.2 This guide is a compilation of the experience of investigators skilled in the art of conducting exfoliation tests and assessing the degree and significance of the damage encountered. The focus is on two general aspects: guides to techniques that will enhance the likelihood of obtaining reliable information, and tips and procedures to avoid pitfalls that could lead to erroneous results and conclusions.  
4.3 The following three areas of testing are considered: the test materials starting with the “as-received” sample up through final specimen preparation, the corrosion test procedures including choice of test, inspection periods, termination point, and rating procedures, and analyses of results and methods for reporting them.  
4.4 This guide is not intended as a specific corrosion test procedure by which to evaluate the resistance to exfoliation of an aluminum alloy product.  
4.5 This guide is not intended as a basis for specifications, nor as a guide for material lot acceptance.
SCOPE
1.1 This guide differs from the usual ASTM standard in that it does not address a specific test. Rather, it is an introductory guide for new users of various standard exfoliation test methods with consideration for specific aluminum alloy families (see Terminology G193 for definition of exfoliation).  
1.2 This guide covers aspects of specimen preparation, exposure, inspection, and evaluation for conducting exfoliation tests on aluminum alloys in both laboratory accelerated environments and in natural, outdoor atmospheres. The intent is to clarify any gaps in existent test methods.  
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2022
• ICS: 77.120.10 - Aluminium and aluminium alloys
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.05 - Laboratory Corrosion Tests

Relations

• Refers: ASTM G66-23 - Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)
• Effective Date: 01-Dec-2023
• Refers: ASTM G34-23 - Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
• Effective Date: 01-Dec-2023
• Refers: ASTM G85-19 - Standard Practice for Modified Salt Spray (Fog) Testing
• Effective Date: 01-Nov-2019
• Refers: ASTM G34-01(2013) - Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
• Effective Date: 01-May-2013
• Refers: ASTM G66-99(2013) - Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)
• Effective Date: 01-May-2013
• Refers: ASTM G1-03(2011) - Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• Effective Date: 01-Dec-2011
• Refers: ASTM G85-11 - Standard Practice for Modified Salt Spray (Fog) Testing
• Effective Date: 01-May-2011
• Refers: ASTM G50-10 - Standard Practice for Conducting Atmospheric Corrosion Tests on Metals
• Effective Date: 01-Sep-2010
• Refers: ASTM G92-86(2010) - Standard Practice for Characterization of Atmospheric Test Sites
• Effective Date: 01-Sep-2010
• Refers: ASTM G85-09 - Standard Practice for Modified Salt Spray (Fog) Testing
• Effective Date: 01-Jul-2009
• Refers: ASTM G34-01(2007) - Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
• Effective Date: 01-May-2007
• Refers: ASTM G66-99(2005)e1 - Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)
• Effective Date: 01-May-2005
• Refers: ASTM G66-99(2005) - Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)
• Effective Date: 01-May-2005
• Refers: ASTM G1-03 - Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• Effective Date: 01-Oct-2003
• Refers: ASTM G85-02e1 - Standard Practice for Modified Salt Spray (Fog) Testing
• Effective Date: 10-Oct-2002

Overview

ASTM G112-22: Standard Guide for Conducting Exfoliation Corrosion Tests in Aluminum Alloys is a comprehensive standard published by ASTM International. This guide serves as an introduction for new users of established exfoliation corrosion test methods applicable to various families of aluminum alloys. Unlike specific test methods, ASTM G112-22 focuses on providing practical guidance related to specimen preparation, exposure conditions, inspection techniques, and evaluation procedures. By compiling the expertise of seasoned investigators, the guide aims to improve consistency, reliability, and relevance of exfoliation testing results, particularly when correlating laboratory accelerated testing with real-world outdoor exposure and end-use performance.

Key Topics

• Context and Purpose: ASTM G112-22 does not replace existing ASTM test methods for exfoliation corrosion but helps users understand potential variables that affect results and the interpretation of data. It emphasizes the importance of selecting suitable tests, understanding specimen characteristics, and correlating results with actual service performance.

• Material Variables: Discusses factors such as grain structure, temper condition, and sample reproducibility. Proper specimen selection and preparation are key to obtaining meaningful results.

• Specimen Preparation: Covers detailed guidelines for preparing aluminum samples, including degreasing, machining, etching, and considerations for clad and non-uniform grain structures.

• Test Method Selection: Offers advice on selecting appropriate ASTM corrosion test methods based on alloy type, intended application, and end-use environment.

• Inspection and Evaluation: Emphasizes both visual and metallographic inspections, as well as periodic monitoring throughout exposure. Introduces classification codes (e.g., N, P, EA-ED for varying degrees of corrosion) for reporting exfoliation severity.

• Data Correlation and Reporting: Highlights the significance of correlating accelerated laboratory test results with outdoor atmospheric exposure to ensure realistic assessment of alloy performance.

• Limitations: ASTM G112-22 is not a specification nor intended for material acceptance, nor does it replace safety, health, or regulatory considerations.

Applications

This standard guide has broad practical value for a range of applications in industries that rely on aluminum alloys, including:

• Aerospace & Transportation: Supports quality assurance and durability evaluations where structural integrity and long-term performance are critical concerns for safety and reliability.

• Construction & Marine: Helps predict the behavior of aluminum components and assemblies exposed to harsh maritime or urban environments, where exfoliation corrosion is a risk.

• Manufacturing & Material Development: Assists R&D teams in benchmarking new alloys or treatments by providing guidance on consistent specimen preparation and evaluation.

• Academic & Laboratory Research: Offers educational insight and recommended practices for corrosion studies, supporting reproducible and valid experimental results.

Related Standards

Several other ASTM standards are referenced within ASTM G112-22 for complementary guidance on test execution and terminology:

• ASTM G34 - Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
• ASTM G66 - Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)
• ASTM G85 - Practice for Modified Salt Spray (Fog) Testing, including MAASTMAASIS, SWAAT, and other specific environments
• ASTM G50 - Practice for Conducting Atmospheric Corrosion Tests on Metals
• ASTM G92 - Practice for Characterization of Atmospheric Test Sites
• ASTM G1 - Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• ASTM G193 - Terminology and Acronyms Relating to Corrosion

By referencing these and following the best practices outlined in ASTM G112-22, users can enhance the reliability, reproducibility, and real-world relevance of exfoliation corrosion testing for aluminum alloys.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G112 − 22
Standard Guide for
Conducting Exfoliation Corrosion Tests in Aluminum Alloys
This standard is issued under the fixed designation G112; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G66Test Method for Visual Assessment of Exfoliation
Corrosion Susceptibility of 5XXX Series Aluminum Al-
1.1 ThisguidediffersfromtheusualASTMstandardinthat
loys (ASSET Test)
it does not address a specific test. Rather, it is an introductory
G85Practice for Modified Salt Spray (Fog) Testing
guide for new users of various standard exfoliation test
G92Practice for Characterization ofAtmospheric Test Sites
methods with consideration for specific aluminum alloy fami-
G193Terminology and Acronyms Relating to Corrosion
lies (see Terminology G193 for definition of exfoliation).
2.2 ASTM Adjunct:
1.2 This guide covers aspects of specimen preparation,
IllustrationsofAppearanceClassifications(6glossyphotos)
exposure,inspection,andevaluationforconductingexfoliation
tests on aluminum alloys in both laboratory accelerated envi-
3. Terminology
ronments and in natural, outdoor atmospheres. The intent is to
3.1 Definitions of Terms Specific to This Standard:
clarify any gaps in existent test methods.
3.1.1 panel, n—a flat, rectangular specimen normally taken
1.3 The values stated in SI units are to be regarded as
with the test surface parallel to the longitudinal and long-
standard. The values given in parentheses after SI units are
transversedimensionsoffabricatedproduct.Forthinsheetand
providedforinformationonlyandarenotconsideredstandard.
extrusions, the thickness may be the full thickness of the part.
1.4 This standard does not purport to address all of the
3.1.2 sample, n—a portion of a large piece, or an entire
safety concerns, if any, associated with its use. It is the
piece out of a group of many pieces, that is submitted for
responsibility of the user of this standard to establish appro-
evaluation and considered representative of the larger piece or
priate safety, health, and environmental practices and deter-
population. For castings and forgings, this may be an extra
mine the applicability of regulatory limitations prior to use.
portion or prolongation, or in the case of small parts, an entire
1.5 This international standard was developed in accor-
extra piece taken from a specific lot.
dance with internationally recognized principles on standard-
3.1.3 specimen, n—the actual test piece to be corrosion
ization established in the Decision on Principles for the
tested. Frequently this has a specific shape with prescribed
Development of International Standards, Guides and Recom-
dimensional tolerances and finishes.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 3.1.4 test plane, n—the plane in the thickness of the sample
that is being tested. Generally this is the fabricated surface or
2. Referenced Documents
somespecifiedinteriorplane.Interiorplanestypicallyusedare:
2.1 ASTM Standards: (a) T/10=10% of the thickness removed, (this is representa-
G1Practice for Preparing, Cleaning, and Evaluating Corro-
tive of a minimal machining cut to obtain a flat surface), (b)
sion Test Specimens T/4=quarter plane, 25% of the thickness removed, and (c)
G34TestMethodforExfoliationCorrosionSusceptibilityin
T/2=midplane, 50% of the thickness removed.
2XXX and 7XXX SeriesAluminumAlloys (EXCO Test)
G50Practice for Conducting Atmospheric Corrosion Tests 4. Significance and Use
on Metals
4.1 Although there are ASTM test methods for exfoliation
testing, they concentrate on specific procedures for test meth-
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
odology itself. Existent test methods do not discuss material
Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory
variables that can affect performance. Likewise they do not
Corrosion Tests.
address the need to establish the suitability of an accelerated
Current edition approved Dec. 1, 2022. Published January 2023. Originally
approvedin1992.Lastpreviouseditionapprovedin2015asG112–92(2015).DOI:
test for alloys never previously tested nor the need to correlate
10.1520/G0112-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from ASTM International Headquarters. Order Adjunct No.
the ASTM website. ADJG003402-E-PDF. Original adjunct produced in 1980.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G112 − 22
results of accelerated tests with tests in outdoor atmospheres sions or die forgings, may have several categories of grain
and with end-use performance. structuresandgrainflowthatdonotnecessarilyfollowthepart
geometry. Grain structure of such parts must be determined by
4.2 This guide is a compilation of the experience of inves-
macroetching or from prior experience.
tigators skilled in the art of conducting exfoliation tests and
5.3.1 For a given temper condition, unrecrystallized,
assessing the degree and significance of the damage encoun-
pancake-shaped grains, that are long and wide but relatively
tered.Thefocusisontwogeneralaspects:guidestotechniques
thin, are the most susceptible. Pancake-shaped recrystallized
that will enhance the likelihood of obtaining reliable
grains, as in sheet, are the next most susceptible. This is
information,andtipsandprocedurestoavoidpitfallsthatcould
followed by the long, rod-shaped grains found in extruded or
lead to erroneous results and conclusions.
rolled rod and bar with a symmetrical cross section, for
4.3 The following three areas of testing are considered: the
example, circle, square, hex, or a rectangle with the width not
testmaterialsstartingwiththe“as-received”sampleupthrough
more than twice the thickness. An equiaxed grain structure is
final specimen preparation, the corrosion test procedures in-
the least susceptible to exfoliation, especially if the grain size
cluding choice of test, inspection periods, termination point,
islarge.Oftentherecrystallizedsurfacelayeronproductssuch
and rating procedures, and analyses of results and methods for
asextrusions,forgings,orsheetwillnotexfoliate,eventhough
reporting them.
it corrodes intergranularly.
4.4 This guide is not intended as a specific corrosion test
5.4 Sample Temper—When a large sample is obtained as a
procedure by which to evaluate the resistance to exfoliation of
stock item for use over a long time period, the extra material
an aluminum alloy product.
should be stored in a stable temper and at a low enough
temperature so that no further precipitation will occur to alter
4.5 This guide is not intended as a basis for specifications,
the starting condition of the metal. The unaged W temper of
nor as a guide for material lot acceptance.
7XXX alloys is not stable and will continue to age harden at
room temperature. Room temperature storage of such material
5. Sample
should be limited to a couple of months at most. Natural aging
5.1 Sample Size—Most exfoliation tests do not require any
ofthesealloyscanberetardedalmostcompletelybystoringthe
particular specimen size but, when beginning a new
materialinafreezerat−40°C(−40°F)orcolder.Thisfactoris
investigation, it is best to obtain considerably more material
of even more importance in determination of mechanical
than the minimum amount needed. About 50% to 100%
properties than the investigation of corrosion resistance. An
overage is recommended. This avoids the need of procuring a
alternative practice is to use a standard first-step age that will
secondsample,thatmayhaveadifferentresponse,tocomplete
stabilizethematerialandallowforvariationsinthesubsequent
any confirmatory retests or extensions to a specific program.
second and third aging steps.
5.2 Sample Reproducibility—The specific location of
samples in a mill product, and the number of samples to take
6. Selection of an ASTM Test Method
are beyond the scope of this guide. When testing large
6.1 SelectionoftheappropriateASTMtestmethod(s)touse
production items, a typical procedure is to test at both ends
will depend primarily on the type of alloy and on the end-use
(front and rear), and to test at the side and at the mid-width if
environment. When testing a new alloy or temper, a test
the product is 0.6 m (2 ft) or more in width. Thick products
methodknowntobeapplicabletothemostsimilarcommercial
should be tested at various planes through the thickness.
alloyisnormallyselected.Theuseriscautioned,however,that
5.2.1 In addition, some assessment should be made of the
even small changes in alloy chemical composition, or changes
uniformity of a large sample, or of numerous small samples.
in processing method (for example, rapid solidification pro-
Typical quick check methods would be to measure electrical
cesses) can markedly effect resistance of an alloy and the
conductivity or hardness. If the material variability has a
appropriatenessofatestmethod.Normallyexfoliationtestsare
pattern, for example, a difference between front and rear of a
conducted on ingot metallurgy alloys, that tend to have the
long extrusion, then this should be noted and the specimens
elongated grain structure prone to exfoliate. The known alloy
segregated accordingly. If the variability is random, then
applicability of the ASTM test methods are listed below.
multiple test specimens should be randomized.
Includedaresomeobservedinstanceswhereatestmethodwas
5.3 Sample Microstructure—The directionality of the grain found to be inappropriate, or at least produced results different
structure of aluminum alloys will markedly affect the suscep- than those observed on the initial qualification alloys.
tibility to exfoliation. When a product shape and alloy are 6.1.1 It is advisable to initially employ more than one
being tested for the first time, it is advisable to macroetch full laboratory test method and determine whether they agree; or if
thickness by longitudinal and by transverse slices to establish not, which method is the most discriminating. One procedure
the directionality and uniformity of the grain structure. Test fordoingthisistoapplydifferentfabricationprocedurestothe
panels are normally positioned such that the test surface is metal that are known to generally affect resistance to exfolia-
parallel to the plane in the product with the most elongated tion and determine which of the test methods best detects
grain structure. Complex shaped parts, such as certain extru- differences in the corresponding resistance to exfoliation.
G112 − 22
Fabrication variables that often affect resistance to exfoliation 6.4.2 The test cabinets used to conduct the MASTMAASIS
are variable quench-cooling rates, slow quenches being ad- test, and the salt fog tests subsequently described in 6.5 and
verse;andvariableamountsofaging,underaged,orpeak-aged 6.6, are produced by several suppliers. The fog delivery
conditions generally being more susceptible than overaged systems and cabinet geometry can differ and have gradually
conditions (1).
evolved. Consequently some cabinet-to-cabinet variability in
test results is inherent, due primarily to variation in spray
6.2 Test Method G66 Acidified Salt Solution Exfoliation
techniques and the relative humidity conditions during the
Test (ASSET) is used for 5XXX alloys containing 2.0% or
non-spray portions of the cycle.
more magnesium. The round-robin qualification tests for this
6.4.3 There is no record of the MASTMAASIS environ-
test method were conducted on alloys 5086 (3.5%Mg to
ment being unrealistically aggressive, causing exfoliation of a
4.5% Mg) and 5456 (4.7%Mg to 5.5% Mg). (2) However,
material that did not subsequently exfoliate in the seacoast.As
Test Method G66 (ASSET) gives problem-free exfoliation
such, any occurrence of exfoliation in this test most likely
indications with all 5XXX alloys.
indicates susceptibility under some service conditions. The
6.3 TestMethodG34ExfoliationCorrosion(EXCO)Testis
converse of this statement has not been observed.
intended for use with high strength 2XXX and 7XXX ingot
6.4.4 MASTMAASIS is not appropriate for 5XXX alloys,
metallurgyalloys,a96hperiodbeingprescribedforthe2XXX
because it does not always detect exfoliation susceptibility in
alloys and a 48 h period for the 7XXX alloys.
materials proven to be susceptible by other test methods.
6.3.1 For the 2XXX alloys, the round-robin qualification
tests were conducted on alloys 2024 and 2124 in theT351 and 6.4.5 MASTMAASIS has been used with some success on
T851tempers.Theappropriatenessofthemethodhasnotbeen 6XXX series alloys. However, in some cases it caused severe
fully established for all other 2XXX alloys. It has been intergranular corrosion that could be confused with exfoliation
reported as being too aggressive and nonrepresentative of corrosion unless specimens are examined metallographically.
performanceinoutdooratmospheresforalloys2219,2419,and
6.5 Annex A3 of Practice G85 Seawater Acetic Acid Test
2519 in the T851 tempers (3) and for various Al-Li alloys in
(SWAAT) was developed using the same 5XXX, 2XXX, and
both as-quenched and artificially aged tempers (1).
7XXX alloys as mentioned above for the ASSET and EXCO
6.3.2 For the 7XXX alloys, the round-robin qualification
methods (7).
tests were conducted on alloy 7075 in the T651, T7651, and
T7351tempersandalloy7178intheT651andT7651tempers. 6.6 Practice G85AnnexA4 (SALT/SO Spray Testing) was
Experience has shown that the EXCO method can be used for developed using the same, 2XXX and 7XXX alloys as men-
7050 and 7150 alloys in the T651, T6151, T7451, T7651, and tioned above for the EXCO method (8).
T7751 tempers, but the test is somewhat more aggressive on
6.7 Both the methods in Annex A3 and Annex A4 of
these alloys (4). This method also was evaluated with copper-
Practice G85 result in more gelatinous corrosion products than
free alloys such as 7021-T6 and 7146-T6, but generally an
doesAnnexA2.This tends to increase pitting corrosion on the
abbreviated exposure period of 16h to 24 h was used.
specimens.AnnexmethodsA2,A3,andA4inPracticeG85are
6.3.3 Exposure of the powder metallurgy alloys 7090 and
not equivalent, and the user should determine which method
7091-T6 specimens to EXCO results in rapid dissolution and
best suits the alloys and applications under investigation.
powdering of the specimen, due to continuous drop of the
extremelyfinegrains.Fouryearsofexposureofthesameparts
7. Baseline Experience
to seacoast atmosphere resulted only in mild general corrosion
and no exfoliation (5).
7.1 The best check on the appropriateness of an accelerated
test is to determine whether the results it produces agree with
6.4 AnnexA2ofPracticeG85ModifiedASTMAceticAcid
known service experience.
Salt Intermittent Spray Test, (MASTMAASIS) was developed
using alloys 2024, 2124, 7075, and 7178. This method usually
7.2 When there is no actual service experience, then expo-
is run in the wet bottom condition (some solution and high
sure in a severe outdoor atmosphere known to produce
humidity always present).Adry bottom condition (no solution
exfoliation corrosion is a useful approximation of the condi-
present and gradually falling humidity during the purge and
tionsapartwillencounterinservice.Themostfrequentlyused
non-spraying periods) has been recommended for 2XXX
environmentsareseacoastsitesandhighlyindustrializedurban
alloys. This reflects experience and controlled tests that show
locations. Selection of the particular environment to use can
7xxx alloys to be more susceptible to wet bottom, but 2xxx
best be based on the intended end use. If there is no prior
alloystobemoresusceptibletodrybottom;infact,wetbottom
experience with the particular alloy being tested, then outdoor
underestimatesseacoastexfoliationsusceptibilityforanumber
tests should be started as soon as possible to establish a
of 2xxx alloys.
baseline for eventual comparison.
6.4.1 Thedrybottomconditionhasbecomethestandardfor
7.3 Seacoast atmospheres are representative of the more
2XXX Al-Li alloys as it has been shown to accurately reflect
extreme conditions most parts can encounter in service.
seacoast performance for numerous Al-Li alloys and tempers
However, it is noteworthy that “SeacoastAtmospheric Condi-
(6).
tions” prevail only in the immediate vicinity of the seashore.
Generally “seacoast” conditions no longer exist after 0.4 km
The boldface numbers in parentheses refer to a list of references at the end of
this standard. (0.25 mile) distance from the shoreline.
G112 − 22
7.3.1 Significant differences have been noted in tests con- method for accelerated tests is to number the back side of the
ducted at the two beach sites at Kure Beach, NC, which are specimen and then mask off that area. A separate tag of a
located 25m and 250 m (80ft and 800 ft) from the shoreline
non-corrodible, non-conducting material is another method.
(9).
8.2.1 On-sitetestsfrequentlyrunformanyyearsandmaybe
7.3.2 AnotableexampleofthiseffectisobservedattheU.S.
evaluatedbyseveralpersons.Itisimportant,therefore,tohave
Army’s exposure sites at Fort Sherman, at the Caribbean
good initial records describing the original material, the
entrance to the Panama Canal. The Breakwater and Coastal
specimens, the test purposes, and the intended periods of
sitesarewithinsightofeachotherandhavebeenphotographed
exposure. Clear records should also be maintained with de-
in one picture. However, the Breakwater site incurs direct
scriptiveremarksordocumentingphotographsforeachinspec-
saltwater spray from wave action of the Caribbean Sea,
tion period.
whereas the Coastal site is about 50 m (165 ft) from the shore
8.3 Specimen Machining—Specimen edges may be sawed
and is protected from wave action by a coral reef. Depending
or machined. If panels are obtained by shearing, the edges
on the season of the year and the length of exposure, corrosion
should be dressed back by machining, sanding, or filing to a
rates of iron and steel were two to nine times higher for the
depth equal to or greater than the specimen thickness. The
Breakwater site compared with the Coastal site (10).
claddingshouldberemovedfromthetestsurfaceofspecimens
7.3.3 Similarly, there can be considerable variation among
fromalcladsheetandeitherremovedormaskedoffontheback
seacoasts sites due to ambient conditions such as temperature,
(non-test) surface. When machining panels for exposure of
humidity, airborne pollutants, and physical layout such as
interiorplanes(T/10,T/2,andsoforth.)thefinalmachiningcut
rocky coasts that increase seawater spray, the shape of the
should be a light one of 0.635 mm (0.025 in.) or less to avoid
coastline, and prevailing wind direction. Controlled studies
having a highly worked surface. The grain structure of such a
have been conducted that show time to develop exfoliation
workedsurfacemaynotexfoliateandinsteadcreateamislead-
varying, but the various sites agreeing on the sample ranking
with respect to exfoliation resistance. (9, 10, 11) ing artifact by peeling off in one layer when the underlying
structure corrodes. For very thick plate and other thick
7.3.4 At least two years’ exposure is needed at a seacoast
site in order to be considered a significant length of exposure. products, a good procedure is to saw off most of the material
and machine only the last 2.5 mm (0.100 in.) or so. If any
Materials with marked susceptibility to exfoliation normally
begin to show some evidence of it within 6months to 24 cosmetic differences (for example, color changes, scratches,
months. Materials showing very mild susceptibility to exfolia- surface roughness, and so forth.) are noted on the as-machined
tion in accelerated tests may require as long as seven to nine surfaces, they should be recorded. Subsequently the investiga-
years of exposure at a seacoast site to develop a similar degree tor should establish whether these visible differences had an
of exfoliation (11). effect on initiation or development of exfoliation.
8.4 Surface Preparation—Specimens should be degreased
8. Specimens
with a suitable solvent, and it is advisable to remove any mill
8.1 Specimen Size—There is no required specimen size or
scale by mechanical methods such as machining or sanding,
shape, but it is advisable not to use too small a specimen since
and so forth, or by appropriate etching.Afrequently used etch
visual inspection is a key interpretation method. Specimens
technique is to etch for 1min in 5% by weight sodium
shouldbeatleast50mm(2in.)longand25mm(1in.)ormore
hydroxide solution at 80°C (175°F), rinse in water, desmut
in width. This surface area permits visual interpretation as to
30sinconcentratednitricacidatroomtemperature,rinsewith
whether any exfoliation is just protruding whiskers of metal,
distilled or deionized water, and air dry.
small flakes, or delamination of strips of metal. Typical sizes
8.5 Specimen Framing—Gu
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G112 − 92 (Reapproved 2015) G112 − 22
Standard Guide for
Conducting Exfoliation Corrosion Tests in Aluminum Alloys
This standard is issued under the fixed designation G112; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide differs from the usual ASTM standard in that it does not address a specific test. Rather, it is an introductory guide
for new users of othervarious standard exfoliation test methods, methods with consideration for specific aluminum alloy families
(see Terminology G15G193 for definition of exfoliation).
1.2 This guide covers aspects of specimen preparation, exposure, inspection, and evaluation for conducting exfoliation tests on
aluminum alloys in both laboratory accelerated environments and in natural, outdoor atmospheres. The intent is to clarify any gaps
in existent test methods.
1.3 The values stated in SI units are to be regarded as the standard. The inch-pound units values given in parentheses are for
information only.after SI units are provided for information only and are not considered standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
G34 Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
G50 Practice for Conducting Atmospheric Corrosion Tests on Metals
G66 Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET
Test)
G85 Practice for Modified Salt Spray (Fog) Testing
G92 Practice for Characterization of Atmospheric Test Sites
G193 Terminology and Acronyms Relating to Corrosion
2.2 ASTM Adjuncts:Adjunct:
Illustrations of Appearance Classifications (6 glossy photos)
This guide is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory Corrosion
Tests.
Current edition approved Nov. 1, 2015Dec. 1, 2022. Published December 2015January 2023. Originally approved in 1992. Last previous edition approved in 20092015
as G112–92(2009).G112–92 (2015). DOI: 10.1520/G0112-92R15.10.1520/G0112-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Available from ASTM International Headquarters. Order Adjunct No. ADJG003402ADJG003402-E-PDF. Original adjunct produced in 1980.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G112 − 22
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 panel—panel, n—a flat, rectangular specimen normally taken with the test surface parallel to the longitudinal and
long-transverse dimensions of fabricated product. For thin sheet and extrusions, the thickness may be the full thickness of the part.
3.1.2 sample—sample, n—a portion of a large piece, or an entire piece out of a group of many pieces, that is submitted for
evaluation and considered representative of the larger piece or population. For castings and forgings, this may be an extra portion
or prolongation, or in the case of small parts, an entire extra piece taken from a specific lot.
3.1.3 specimen—specimen, n—the actual test piece to be corrosion tested. Frequently this has a specific shape with prescribed
dimensional tolerances and finishes.
3.1.4 test plane—plane, n—the plane in the thickness of the sample that is being tested. Generally this is the fabricated surface
or some specified interior plane. Interior planes typically used are: (a) T/10 = 10 % of the thickness removed, (this is representative
of a minimal machining cut to obtain a flat surface), (b) T/4 = quarter plane, 25 % of the thickness removed, and (c)
T/2 = midplane, 50 % of the thickness removed.
4. Significance and Use
4.1 Although there are ASTM test methods for exfoliation testing, they concentrate on specific procedures for test methodology
itself. Existent test methods do not discuss material variables that can affect performance. Likewise they do not address the need
to establish the suitability of an accelerated test for alloys never previously tested nor the need to correlate results of accelerated
tests with tests in outdoor atmospheres and with end use end-use performance.
4.2 This guide is a compilation of the experience of investigators skilled in the art of conducting exfoliation tests and assessing
the degree and significance of the damage encountered. The focus is on two general aspects: guides to techniques that will enhance
the likelihood of obtaining reliable information, and tips and procedures to avoid pitfalls that could lead to erroneous results and
conclusions.
4.3 The following three areas of testing are considered: the test materials starting with the “as-received” sample up through final
specimen preparation, the corrosion test procedures including choice of test, inspection periods, termination point, and rating
procedures, and analyses of results and methods for reporting them.
4.4 This guide is not intended as a specific corrosion test procedure by which to evaluate the resistance to exfoliation of an
aluminum alloy product.
4.5 This guide is not intended as a basis for specifications, nor as a guide for material lot acceptance.
5. MaterialSample
5.1 Sample Size—Most exfoliation tests do not require any particular specimen size, butsize but, when beginning a new
investigation, it is best to obtain considerably more material than the minimum amount needed. About 5050 % to 100 % overage
is recommended. This avoids the need of procuring a second sample, that may have a different response, to complete any
confirmatory retests or extensions to a specific program.
5.2 Sample Reproducibility—The specific location of samples in a mill product, and the number of samples to take are beyond the
scope of this guide. When testing large production items, a typical procedure is to test at both ends (front and rear), and to test
at the side and at the mid-width if the product is 0.6 m (2 ft) or more in width. Thick products should be tested at various planes
through the thickness.
5.2.1 In addition, some assessment should be made of the uniformity of a large sample, or of numerous small samples. Typical
quick check methods would be to measure electrical conductivity or hardness. If the material variability has a pattern, for example,
a difference between front and rear of a long extrusion, then this should be noted and the specimens segregated accordingly. If the
variability is random, then multiple test specimens should be randomized.
G112 − 22
5.3 Sample Microstructure—The directionality of the grain structure of aluminum alloys will markedly affect the susceptibility to
exfoliation. When a product shape and alloy are being tested for the first time, it is advisable to macroetch full thickness by
longitudinal and by transverse slices to establish the directionality and uniformity of the grain structure. Test panels are normally
positioned such that the test surface is parallel to the plane in the product with the most elongated grain structure. Complex shaped
parts, such as certain extrusions or die forgings, may have several categories of grain structures and grain flow that do not
necessarily follow the part geometry. Grain structure of such parts must be determined by macroetching or from prior experience.
5.3.1 For a given temper condition, unrecrystallized, pancake shaped pancake-shaped grains, that are long and wide but relatively
thin, are the most susceptible. Pancake shaped Pancake-shaped recrystallized grains, as in sheet, are the next most susceptible. This
is followed by the long, rod shaped rod-shaped grains found in extruded or rolled rod and bar with a symmetrical cross section,
for example, circle, square, hex, or a rectangle with the width not more than twice the thickness. An equiaxed grain structure is
the least susceptible to exfoliation, especially if the grain size is large. Often the recrystallized surface layer on products such as
extrusions, forgings, or sheet will not exfoliate, even though it corrodes intergranularly.
5.4 Sample Temper—When a large sample is obtained as a stock item for use over a long time period, the extra material should
be stored in a stable temper and at a low enough temperature so that no further precipitation will occur to alter the starting condition
of the metal. The unaged W temper of 7XXX alloys is not stable and will continue to age harden at room temperature. Room
temperature storage of such material should be limited to a couple of months at most. Natural aging of these alloys can be retarded
almost completely by storing the material in a freezer at −40°C (−40°F)at −40 °C (−40 °F) or colder. This factor is of even more
importance in determination of mechanical properties than the investigation of corrosion resistance. An alternative practice is to
use a standard first-step age that will stabilize the material and allow for variations in the subsequent second and third aging steps.
6. Selection of an ASTM Test Method
6.1 Selection of the appropriate ASTM test method(s) to use will depend primarily on the type of alloy and on the end use end-use
environment. When testing a new alloy or temper, a test method known to be applicable to the most similar commercial alloy is
normally selected. The user is cautioned, however, that even small changes in alloy chemistry, chemical composition, or changes
in processing method (for example, rapid solidification processes) can markedly effect resistance of an alloy and the
appropriateness of a test method. Normally exfoliation tests are conducted on ingot metallurgy alloys, that tend to have the
elongated grain structure prone to exfoliate. The known alloy applicability of the ASTM test methods are listed below. Included
are some observed instances where a test method was found to be inappropriate, or at least produced results different than those
observed on the initial qualification alloys.
6.1.1 It is advisable to initially employ more than one laboratory test method and determine whether they agree; or if not, which
method is the most discriminating. One procedure for doing this is to apply different fabrication procedures to the metal that are
known to generally affect resistance to exfoliation and determine which of the test methods best detects differences in the
corresponding resistance to exfoliation. Fabrication variables that often affect resistance to exfoliation are variable quench cooling
quench-cooling rates, slow quenches being adverse; and variable amounts of aging, underaged, or peak aged peak-aged conditions
generally being more susceptible than overaged conditions (1).
6.2 Test Method G66 AcidifiedAcidified Salt Solution Exfoliation Test (ASSET) is used for 5XXX alloys containing 2.0 % or
more magnesium. The round robin round-robin qualification tests for this test method were conducted on alloys 5086
(3.5(3.5 % Mg to 4.5 % Mg) and 5456 (4.7(4.7 % Mg to 5.5 % Mg). (2) However, Test Method G66 (ASSET) gives problem free
problem-free exfoliation indications with all 5XXX alloys.
6.3 Test Method G34 Exfoliation Corrosion (EXCO) Test is intended for use with high strength 2XXX and 7XXX ingot
metallurgy alloys, a 96 h period being prescribed for the 2XXX alloys and a 48 h period for the 7XXX alloys.
6.3.1 For the 2XXX alloys, the round robin round-robin qualification tests were conducted on alloys 2024 and 2124 in the T351
and T851 tempers. The appropriateness of the method has not been fully established for all other 2XXX alloys. It has been reported
as being too aggressive and nonrepresentative of performance in outdoor atmospheres for alloys 2219, 2419, and 2519 in the T851
tempers (3) and for various Al-Li alloys in both as-quenched and artificially aged tempers (1).
6.3.2 For the 7XXX alloys, the round robin round-robin qualification tests were conducted on alloy 7075 in the T651, T7651, and
The boldface numbers in parentheses refer to a list of references at the end of this standard.
G112 − 22
T7351 tempers and alloy 7178 in the T651 and T7651 tempers. Experience has shown that the EXCO method can be used for 7050
and 7150 alloys in the T651, T6151, T7451, T7651, and T7751 tempers, but the test is somewhat more aggressive on these alloys
(4). This method also was evaluated with copper free copper-free alloys such as 7021-T6 and 7146-T6, but generally an
abbreviated exposure period of 1616 h to 24 h was used.
6.3.3 Exposure of the powder metallurgy alloys 7090 and 7091-T6 specimens to EXCO results in rapid dissolution and powdering
of the specimen, due to continuous drop of the extremely fine grains. Four years of exposure of the same parts to seacoast
atmosphere resulted only in mild general corrosion and no exfoliation (5).
6.4 Annex A2 of Practice G85 ModifiedModified ASTM Acetic Acid Salt Intermittent Spray Test, (MASTMAASIS) was
developed using alloys 2024, 2124, 7075, and 7178. This method usually is run in the wet bottom condition (some solution and
high humidity always present). A dry bottom condition (no solution present and gradually falling humidity during the purge and
non-spraying periods) has been recommended for 2XXX alloys. This reflects experience and controlled tests that show 7xxx alloys
to be more susceptible to wet bottom, but 2xxx alloys to be more susceptible to dry bottom; in fact, wet bottom underestimates
seacoast exfoliation susceptibility for a number of 2xxx alloys.
6.4.1 The dry bottom condition has become the standard for 2XXX Al-Li alloys as it has been shown to accurately reflect seacoast
performance for numerous Al-Li alloys and tempers (6).
6.4.2 The test cabinets used to conduct the MASTMAASIS test, and the salt fog tests subsequently described in 6.5 and 6.6, are
produced by several suppliers. The fog delivery systems and cabinet geometry can differ and have gradually evolved. Consequently
some cabinet to cabinet cabinet-to-cabinet variability in test results is inherent, due primarily to variation in spray techniques and
the relative humidity conditions during the non-spray portions of the cycle.
6.4.3 There is no record of the MASTMAASIS environment being unrealistically aggressive, causing exfoliation of a material that
did not subsequently exfoliate in the seacoast. As such, any occurrence of exfoliation in this test most likely indicates susceptibility
under some service conditions. The converse of this statement has not been observed.
6.4.4 MASTMAASIS is not appropriate for 5XXX alloys, because it does not always detect exfoliation susceptibility in materials
proven to be susceptible by other test methods.
6.4.5 MASTMAASIS has been used with some success on 6XXX series alloys. However, in some cases it caused severe
intergranular corrosion that could be confused with exfoliation corrosion unless specimens are examined metallographically.
6.5 Annex A3 of Practice G85 Seawater Acetic Acid Test (SWAAT) was developed using the same 5XXX, 2XXX, and 7XXX
alloys as mentioned above for the ASSET and EXCO methods (67).
6.6 Practice G85 Annex A4 (SALT/SO Spray Testing) was developed using the same, 2XXX and 7XXX alloys as mentioned
above for the EXCO method (78).
6.7 Both the methods in Annex A3 and Annex A4 of Practice G85 result in more gelatinous corrosion products than does Annex
A2. This tends to increase pitting corrosion on the specimens. Annex methods A2, A3, and A4 in Practice G85 are not equivalent,
and the user should determine which method best suits the alloys and applications under investigation.
7. Baseline Experience
7.1 The best check on the appropriateness of an accelerated test is to determine whether the results it produces agree with known
service experience.
7.2 When there is no actual service experience, then exposure in a severe outdoor atmosphere known to produce exfoliation
corrosion is a useful approximation of the conditions a part will encounter in service. The most frequently used environments are
seacoast sites and highly industrialized urban locations. Selection of the particular environment to use can best be based on the
intended end use. If there is no prior experience with the particular alloy being tested, then outdoor tests should be started as soon
as possible to establish a baseline for eventual comparison.
7.3 Seacoast atmospheres are representative of the more extreme conditions most parts can encounter in service. However, it is
G112 − 22
noteworthy that “Seacoast Atmospheric Conditions” prevail only in the immediate vicinity of the seashore. Generally “seacoast”
conditions no longer exist after 0.4 Kmkm (0.25 mile) distance from the shoreline.
7.3.1 Significant differences have been noted in tests conducted at the two beach sites at Kure Beach, NC, which are located
2525 m and 250 m (80(80 ft and 800 ft) from the shoreline (89).
7.3.2 A notable example of this effect is observed at the U.S. Army’sArmy’s exposure sites at Fort Sherman, at the Caribbean
entrance to the Panama Canal. The Breakwater and Coastal sites are within sight of each other and have been photographed in one
picture. However, the Breakwater site incurs direct saltwater spray from wave action of the Caribbean Sea, whereas the Coastal
site is about 50 m (165 ft) from the shore and is protected from wave action by a coral reef. Depending on the season of the year
and the length of exposure, corrosion rates of iron and steel were two to nine times higher for the Breakwater site compared with
the Coastal site (910).
7.3.3 Similarly, there can be considerable variation among seacoasts sites due to ambient conditions such as temperature, humidity,
airborne pollutants, and physical layout such as rocky coasts that increase seawater spray, the shape of the coastline, and prevailing
wind direction. Controlled studies have been conducted that show time to develop exfoliation varying, but the various sites
agreeing on the sample ranking with respect to exfoliation resistance. (9, 10, 11)
7.3.4 At least two yearsyears’ exposure is needed at a seacoast site in order to be considered a significant length of exposure.
Materials with marked susceptibility to exfoliation normally begin to show some evidence of it within 66 months to 24 months.
Materials showing very mild susceptibility to exfoliation in accelerated tests may require as long as seven to nine years of exposure
at a seacoast site to develop a similar degree of exfoliation (1011).
8. Specimens
8.1 Specimen Size—There is no required specimen size or shape, but it is advisable not to use too small a specimen since visual
inspection is a key interpretation method. Specimens should be at least 50 mm (2 in.) long and 25 mm (1 in.) or more in width.
This surface area permits visual interpretation as to whether any exfoliation is just protruding whiskers of metal, small flakes, or
delamination of strips of metal. Typical sizes are: 3838 mm to 5050 mm by 100 mm (1.5(1.5 in. or 22 in. by 4 in.) for the Test
Method G34 EXCO test, and the Test Method G66 ASSET test, 7575 mm by 150 mm (3(3 in. by 6 in.) for the Practice G85
Modified Salt Fog tests, Annex A.2A2 (MASTMAASIS), A.3A3 (SWAAT) and A.4A4 (SALT/SO ), and 100100 mm by
150150 mm to 300 mm (4(4 in. by 66 in. to 12 in.) or larger for outdoor atmospheric tests.
8.1.1 Specimens from product forms with non-uniform grain structures, such as extrusions, rod, bar, and forgings, must be large
enough to encompass all relevant grain flow regions. In some cases, the initial test plan may need to include multiple locations
to determine whether severity varies among the locations. Subsequent testing would only need to sample the most susceptible site
or sites.
8.2 Specimen Identification and Records—Considerable material may be lost in the testing of susceptible materials, so scribed or
stenciled specimen numbers often are inadequate. Some sort of permanent identification should be used. One method for
accelerated tests is to number the back side of the specimen and then mask-off mask off that area. A separate tag of a
non-corrodible, non-conducting material is another method.
8.2.1 On-site tests frequently run for many years and may be evaluated by several persons. It is important, therefore, to have good
initial records describing the original material, the specimens, the test purposes, and the intended periods of exposure. Clear records
should also be maintained with descriptive remarks or illustrativedocumenting photographs for each inspection period.
8.3 Specimen Machining—Specimen edges may be sawed or machined. If panels are obtained by shearing, the edges should be
dressed back by machining, sanding, or filing to a depth equal to or greater than the specimen thickness. The cladding should be
removed from the test surface of specimens from alclad sheet and either removed or masked off on the back (non-test) surface.
When machining panels for exposure of interior planes (T/10, T/2, and so forth.) the final machining cut should be a light one of
0.635 mm (0.025 in.) or less to avoid having a highly worked surface. The grain structure of such a worked surface may not
exfoliate and instead create a misleading artifact by peeling off in one layer when the underlying structure corrodes. For very thick
plate and other thick products, a good procedure is to saw off most of the material and machine only the last 2.5 mm (0.100 in.)
or so. If any cosmetic differences (for example, color changes, scratches, surface roughness, and so forth.) are noted on the
as-machined surfaces, they should be reco
...